1. Field of the Invention
The invention relates generally to seismic shear wave vibrators and, more particularly, but not by way of limitation, it relates to improvements in vibrator and transport structure that enables more efficient shear wave energy coupling into an earth medium, particularly a soft earth medium such as might be encountered in marshy areas or water bottoms.
2. Description of the Prior Art
Applicant is aware of a number of different attempts to generate shear wave energy. Early structures attempted shear wave generation by simple impulsive striking of knife-edge structures in order to generate shear waves of requisite polarity. Polarity was selectively controlled simply by orientation of the knife-edge relative to the earth medium. Sometime later, as full value and benefit of shear wave usage became known, various attempts were made at generation of shear waves on both land and sea bottom by both vibratory and explosive or other implusive devices. In general, the prior vibratory devices were coupled through a flat, earth-engaging baseplate which may include various types of cleat or ridge coupling structure. Still other forms of source attempted energy engagement using a knife-edge type of device and this form of energy coupling was found to be particularly desirable in attempts to generate shear waves in watercovered areas.